1. Field of the Invention
The present invention relates to a copper-based material used as a decorative material or as a conductive material, in which, by providing a thin surface treatment layer composed of a metal element different from copper on the surface of a copper or copper alloy base, discoloration and oxidation of the surface can be suppressed, and a method for producing the same.
2. Description of the Related Art
In everyday life, there are various goods (houses, furniture, cars, home appliances, tools, luxury goods, accessories, daily goods, and the like). The factors that determine the values of these goods include, in addition to practicality and functionality, the aesthetic aspect. In decorative items in which the aesthetic aspect is important, shape, color, gloss, and the like are factors that enhance the values of such decorative items. Pure copper-based materials, whose pale pink color and shine have been appreciated for a long time, have been used as decorative materials.
Furthermore, since copper has a high electrical conductivity, second only to silver, it has been used as various conductive members, such as cables. Typical examples of a pure copper-based conductor include oxygen-free copper and tough pitch copper. Pure copper-based conductors are used as a wire-shaped or sheet-shaped material or as plating.
By applying an anticorrosive, such as benzotriazole, to the surface of copper materials for decorative use, oxidation of the copper materials is suppressed. When such copper materials are left to stand in an atmospheric environment, their color and shine degrade with time, and the original aesthetic aspect of pure copper is lost. In the case of copper, an initial oxide film which is a natural oxide film with a thickness of several nanometers is generated. After that, even an increase in the thickness of the oxide film to several tens of nanometers would change the color tone of the exterior markedly and degrade the shine. The reason for this is that oxides mainly containing copper and oxygen bonded to each other (Cu2O and CuO) are formed on the surface of the copper, and the thickness of the resulting oxide film increases with time.
On the other hand, a way of improving the corrosion resistance has been proposed in which a copper material is alloyed by adding an additive element. Furthermore, there has been proposed a method for producing a copper-based member having corrosion resistance in which the surface of a copper material is subjected to zinc (Zn) plating, and then diffusion treatment is performed to form a copper-zinc (Cu—Zn) layer having a zinc (Zn) concentration of 10% to 40% (for example, refer to Japanese Unexamined Patent Application Publication No. 62-040361).
However, as a result of studies by the present inventors, it has been found that, even when such a copper-based member is used, for example, in the case where the copper-based member is used as cable conductors for power and signal transmission for automobile or vehicle use in which the ambient temperature or the sum of the ambient temperature and the operating temperature is 100° C. or higher, the performance required for products, i.e., corrosion resistance (oxidation resistance) for high-temperature, long-term use, is still not completely satisfactory.
Furthermore, in recent years, it has been reported that since amorphous alloys have a structure in which atoms are densely packed, they exhibit excellent corrosion resistance (for example, refer to International Publication No. 2007/108496, and Japanese Unexamined Patent Application Publication Nos. 2008-045203, 2004-176082, 2001-059198, and 2010-163641).
Although amorphous alloys are advantageous in terms of excellent corrosion resistance, they have a drawback in that, since it is necessary to use materials that have been alloyed using a plurality of metal elements, the production process becomes complicated. Techniques for forming amorphous layers using non-alloy zinc have not been fully studied yet.